I. Field of the Invention
The present invention relates to packing element for a biological filter or for use in mass transfer wherein the liquid or gas to be purified is arranged to flow along the trickling faces of said packing element in contact with another medium, e.g. oxidizing air, said trickling faces having relatively large wet surface areas and being arranged at an angle of about 3.degree.-40.degree., preferably 5.degree.-15.degree. with respect to the vertical axes of the element. This packing element can also be used in flue gas washing towers and in distillation columns.
II. Description of the Prior Art
Operation of a biological filter is based on the activity of micro-organisms occurring on the surface of the packing element in a filter. The effluent to be purified is evenly distributed upon the biological filter for packing elements. Effluent trickles down the surface and comes into intimate contact with upwardly flowing air.
A biological filter can be employed as a pretreatment stage or an actual biological treatment depending on loading. A biological filter system can be made more complete with chemical treatment.
Filters of the past were usually filled with rocks but those have been discarded mainly because of their poor efficiency, clogging hazard and great weight.
A more extensive application of biological filters has heterofore been impeded by the high price of filter material. However, plastic packing elements or bodies have changed this situation and made the use of biological filters more economical.
British Patent publication No. 1 498 360 discloses a plastic packing element comprising a cylindrical body fitted with a plurality of inclined ring elements mounted within each other. Since these packing elements are intended to be introduced into a filter vessel quite randomly, said ring elements are provided with relatively large openings and voids so that liquid can trickle as freely as possible through the layer formed by said packing elements. This means, however, that there will be no intact surfaces of any substantial size in any of the packing elements along which liquid could trickle in contact with oxidizing air.
British Patent publication No. 1 439 745 discloses a filter packing element comprising a cylinder or tube member which is provided with various spacing and filling means and whose wall can be perforated. The cylinder is of relatively great length and the fitting thereof in a filter may cause clogging of the flow.